Thermoplastic polyurethanes, polyureas, and polyurethaneureas represent an important family of segmented block copolymer thermoplastic elastomers. They can be extruded, injection or compression molded, or solution spun. They offer a broad range of physical properties and characteristics, including high tensile and tear strength, chemical and abrasion resistance, good processability, and protective barrier properties. Polyurethanes are the most commonly used materials in the production of biomedical devices that come in contact with blood such as pacemakers, defibrillators, angioplasty balloons, surgical drains, dialysis devices, etc.
Depending on composition, i.e. on the volume fraction of the soft, elastomeric segments, these polymers can be soft and rubbery, or hard and rigid materials. The hard segments of polyurethanes or polyureas are composed of diisocyanate and a small molecule diol or diamine chain extender. These hard segments may comprise, for example, diamines and a combination of diols and diamines, respectively, in addition to diisocyanate. The soft segments are mostly low molecular weight polymeric diols, which may include polyester diols, polyether diols, and polydiene diols.
Polyurethanes that incorporate a polyether diol into the soft segment generally suffer long-term in vivo bioinstability due to oxidation of the polyether soft segment, especially when in contact with metals, which catalyze oxidative degradation. This deficiency limits the use of polyurethanes for long-term applications.
Polyisobutylene (PIB)-based thermoplastic polyurethanes (TPUs) offer high thermal, oxidative, and hydrolytic stability, but exhibit insufficient mechanical properties without the addition of a polyether or polyester diol. The need for a PIB-based TPU that exhibits sufficient mechanical properties and biostability is still present.